Field of the Invention
The present invention relates to an alarm processing circuit which can be built and suitably used in an intelligent power module (IPM) etc.
Description of the Background Art
JP-A-H05-300752 discloses a technique in which a plurality of alarm signals sent from a plurality of abnormal current determination portions is inputted to an OR gate and an output signal of the OR gate is outputted as a single abnormal current alarm signal to the outside.
On the other hand, JP-A-2009-142016 discloses a technique in which two signals (one signal for setting a threshold and the other signal for driving a switching element) inputted from the outside are transmitted to a power conversion circuit through one photocoupler in a time division manner.
The technique described in JP-A-H05-300752 has a function only to identify whether any of the alarm signals has occurred or not. Therefore, there is a disadvantage that it is impossible to know which factor caused the alarm signal to occur.
On the other hand, the technique described in JP-A-2009-142016 can indeed contribute to reduction of the number of input terminals (the number of photocouplers to be used), but it is used for transmission of regular signals which are not alarm signals. Therefore, it is a matter of course that the technique does not have a function of determining which one of the alarm signals has occurred. Moreover, the technique can separate two signals on the assumption that the two signals are always transmitted in predetermined forms and at predetermined timings. Therefore, there is a disadvantage that the technique cannot be applied to signals such as alarm signals which cannot be known as to when they will occur.